Device for manufacturing magnetically anisotropic bodies



April 16, 1963 s ETAL 3,085,291

DEVICE FOR MANUFACTURING MAGNETICALLY ANISOTROPIC BODIES Filed Oct. 31. 1960 lNVENTORS EDUARO J. HAES FRITS TOMHOLT 3,085,291 Patented Apr. 16, 1963 3,085,291 DEVICE FOR MANUFACTURING MAGNETI- CALLY ANISOTROPIC BODIES Eduard Johan Haes and Frits Tomholt, Eindhoven,

Netherlands, assignors to North American Philips Company, Inc., New York, N.Y., a corporation of Delaware Filed Oct. 31, 1960, Ser. No. 66,015

6 Claims. (Cl. 18-165) This invention relates to a device for manufacturing magnetically anisotropic bodies by compressing magnetically anisotropic particles in a die of substantially non-ferromagnetic material between the poles of an electromagnet which, if desired, may also serve as Stampers, and sintering the thus obtained conglomerate to a compact body.

Magnetically anisotropic permanent magnets can be manufactured by compressing small, magnetically anisotropic particles of a ferromagnetic material of the formula Ba Sr Pb O.6Fe O (in which formula x+y+z= l while in a mobile state, i.e. free to move in a strong magnetic field, by which they are also oriented magnetically. The thus oriented particles can then be sintered to a magnetically anisotropic permanent magnetic body.

Compression is preferably carried out in a device which is provided with one or more dies of substantially nonferromagnetic material and with an electromagnet. In one form, i.e. wet pressing, the finely divided ferromagnetic substance is suspended in an inert liquid, the die containing auxiliary means for supplying this liquid. In another form, i.e., dry pressing, the ferromagnetic particles in the die are vibrated as long as possible.

The drawback of the above-described compression methods is that the magnets obtained by sintering the oriented powder often show cracks and fissures especially at their surface, so that the percentage of rejects in the manufacture sometimes is rather high. This is the case especially when a compression device is used in which it is possible to compress powder simultaneously in several dies which are collectively surrounded by the coil of an electromagnet.

It is an object of this invention to provide a device for compressing the powder for a magnetically anisotropic magnet so that after the compressed powder is sintered, substantially no cracks or fissures develop in the magnet.

These and further objects of the invention will appear as the specification progresses.

In accordance with our invention, we have unexpectedly found that fissures and cracks which occur after sintering can be reduced or eliminated if the powder is compressed in a die of substantially non-ferromagnetic material between poles of a magnet, the ends which, in contact with the powder, are constituted of a non-ferro magnetic material, e.g. brass, plastic, non-metallic alloys, and the like. We do not know for what reason the fissures and cracks are reduced or eliminated by employing non-ferromagnetic ends of the poles for compressing the powder, but we have found that when such poles are used, the percentage of rejects is materially reduced.

The invention will be described with reference to the accompanying drawing, the sole FIGURE of which shows a compression device in section for manufacturing magnetically anisotropic ferromagnetic bodies according to the invention.

In the device shown in the drawing, ferromagnetic ma terial 1, of the composition Ba Sr Pb O.6Fe O (in which formula x+y+-:1), and in the form of particles, by far the greater part of which is of such a high degree of fineness as to provide for a strong magnetic anisotropy of the individual particles, is contained within die 2. Die 2 is constituted of, for example, brass or aluminium-brass, and is surrounded by a coil 3 of an electromagnet, the poles 4 and 5 of which are made of ferromagnetic material, for example maehinable steel, the latter serving as Stampers as well. Consequently, the material in the die is compressed as well as oriented simultaneously.

In order to keep the particles mobile during the orientation and compression operation, they are suspended in an inert liquid, such as water, which is removed during compression, for example by way of lower stamper 5 provided at its upper end by a sieve plate 8 which filters the liquid through apertures 9 and channel 10 in stamper 5 but does not permit passage of the particles.

Stampers 4 and 5 are provided with end pieces 6 and 7 of non-ferromagnetic material, e.g., brass, aluminiumbrass, non-ferromagnetic alloys, plastics, and the like, of sufiicient strength and hardness to compress the particles.

After the material is magnetically oriented and compressed in the die by the Stampers, the molded body is removed from the die and sintered at a temperature of about 1100 to 1350 C., at which temperature the particles unite and form a coherent body. It is during sintcring that cracks and fissures form, but if the powder has been compressed between poles the ends of which are constituted of a non-ferromagnetic material, not only is the body magnetically anisotropic, i.e. it has a preferred direction of magnetization because the individual particles are aligned in mutually parallel directions, but the sintered body does not exhibit cracks or fissures.

For example, it has been found that reject rate of magnets manufactured in accordance with the invention was 2 to 6% as compared to to using conventional stampers of ferromagnetic material only.

The invention may also be used where a plurality of dies are surrounded by a single coil, provided the stampers for each die have ends which are constituted of a non-ferromagnetic material. This is highly advantageous because several magnets may be thus manufactured simultaneously.

The invention also may be employed in the manufacture of anisotropic permanent magnet bodies of the composition Ba Sr Pb O.6Fe O (in which formula in which a mixture of fine, magnetically anisotropic particles of said composition and a plurality of finelydivided metal oxides capable of reacting, upon sintering, to form a material, the composition of which is likewise in accordance with said formula, is compressed in a magnetic field and subsequently sintered at a temperature of about 1160 to 1400 C., as disclosed in US. Patent 2,837,483. A further possibility of using the invention is in the method of compressing a finely-divided initial mixture of metaloxidic compounds, the particles of at least one of which are capable of being oriented magnetically, in a magnetic field and sintering the agglomerate thus obtained, to form a magnetically anisotropic body consisting of a material that was not present in the initial mixture just referred to. The method of manufacturing such bodies (which may be built up from materials, the unit crystals of which have a preferred plane of magnetization) is described in US. application Serial No. 734,727, filed May 12, 1958, by E. W. Gorter et al., and assigned to the assignee of the instant application.

While we have described the invention in connection with a specific embodiment, and specific applications thereof, other modifications will be readily apparent to those skilled in the art without departing from the spirit and scope of the invention which is defined in the appended claims.

What is claimed is:

1. Apparatus for molding and magnetically orienting a finely-divided ferromagnetic material into a body which is thereafter sintered comprising a pair of opposed spaced ferromagnetic members having non-ferromagnetic end portions between which the finely-divided ferromagnetic material can be compressed, means to produce an orienting magnetic field between said spaced members, and means to compress the finely-divided material between the spaced members.

2. Apparatus for molding and magnetically orienting a finely-divided ferromagnetic material suspended in a liquid into a body which is thereafter sintered comprising a pair of opposed spaced ferromagnetic members having non-ferromagnetic end portions between which the finelydivided ferromagnetic material can be compressed, means to produce an orienting magnetic field between said spaced members, means to compress the finely-divided material between the spaced members, and means to remove the liquid during compression of the finely-divided ferromagnetic material.

3. Apparatus for molding and magnetically orienting a finely-divided ferromagnetic material into a body which is thereafter sintered comprising a pair of opposed spaced ferromagnetic members having brass end portions between which the finely-divided ferromagnetic material can be compressed, means to produce an orienting magnetic field between said spaced members, and means to compress the finely-divided material between the pole members.

4. Apparatus for molding and magnetically orienting a finely-divided ferromagnetic material into a body which is thereafter sintered comprising a pair of opposed spaced ferromagnetic members having non-ferromagnetic end portions constituted of a plastic material between which the finely-divided ferromagnetic material can be compressed, means to produce an orienting magnetic field between the spaced members, and means to compress the finely-divided material between the spaced members.

5. Apparatus for molding and magnetically orienting a finely-divided ferromagnetic material into a body which is thereafter sintered comprising a pair of opposed spaced magnetic pole members having non-ferromagnetic end portions between which the finely-divided ferromagnetic material can be compressed, means to energize said magnetic pole members to produce a magnetic field therebetween, and means to compress the finely-divided material between the energized pole members.

6. Apparatus for molding and magnetically orienting a finely-divided ferromagnetic material into a body which is thereafter sintered comprising a die for receiving the finely-divided ferromagnetic material, a pair of opposed moveable members for compressing the finely-divided ferromagnetic material while in said die, each of said moveable members having a portion constituted of a ferromagnetic material and a portion in contact with the material in said die which is constituted of a non-ferromagnetic material, and means associated with said moveable members for producing magnetic poles in said ferromagnetic portions and a magnetic field between said moveable members.

References Cited in the file of this patent UNITED STATES PATENTS 2,026,940 Hendryx Jan. 7, 1936 2,033,735 Pack Mar. 10, 1936 2,437,127 Richardson Mar. 2, 1948 2,448,277 Renier Aug. 31, 1948 2,964,793 Blume Dec. 20, 1960 

1. APPARATUS FOR MOLDING AND MAGNETICALLY ORIENTING A FINELY-DIVIDED FERROMAGNETIC MATERIAL INTO A BODY WHICH IS THEREAFTER SINTERED COMPRISING A PAIR OF OPPOSED SPACED FERROMAGNETIC MEMBERS HAVING NON-FERROMAGNETIC END PORTIONS BETWEEN WHICH THE FINELY-DIVIDED FERROMAGNETIC MATERIAL CAN BE COMPRESSED, MEANS TO PRODUCE AN ORIENTING MAGNETIC FIELD BETWEEN SAID SPACED MEMBERS, AND MEANS TO COMPESS THE FINELY-DIVIDED MATERIAL BETWEEN THE SPACED MEMBERS. 